Beam with varied bending moment, apparatus, and method

ABSTRACT

A structural beam includes a reinforcement beam having a length and mounts at ends of the beam and cross sectional shapes at various locations along the length, including a first cross sectional shape near ends of the beam providing a first bending moment and a second cross sectional shape at a center of the beam providing a second bending moment different than the first bending moment, and further including intermediate cross sectional shapes between the ends and center having intermediate bending moments between the first and second bending moments. The cross sections may define open C-shapes or may include a tubular shape.

This application claims benefit under 35 USC section 119(e) of U.S.Provisional Application Ser. No. 61/889,750, filed Oct. 11, 2013,entitled BEAM WITH VARIED BENDING MOMENT, APPARATUS, AND METHOD, theentire disclosure which is hereby incorporated by reference in itsentirety.

BACKGROUND

The present invention relates to structural beams used as bumperreinforcement beams in vehicle bumper systems, although the presentinnovation is not limited to only vehicle bumper systems.

Many reinforcement beams in vehicle bumper systems are roll formed, dueto the advantages in high volume of dimensional consistency and lowcost. In roll forming processes, a sheet is typically rolled into aconstant cross section (e.g. tubular or open channel) and then cut tolength. Sometimes the beam is longitudinally curved (called “sweeping”)as part of the roll forming process or as a secondary operation afterthe roll forming process. For example, see Sturrus U.S. Pat. Nos.5,454,504, and 5,104,026 and 6,240,820. Low weight and highstrength-to-weight ratio are important properties in bumperreinforcement beams since heavier vehicles get lower gas mileage andtend to emit greater amounts of pollution. Further, lower weight canmean less material and lower part costs. However, an improvement isdesired that maintains functional requirements of a particular bumperreinforcement beam, but that reduces weight and provides optimizedstrength-to-weight ratio. Also, an improvement is desired that optimizestorsional and bending strength in longitudinal areas along a length ofthe beam while minimizing weight.

SUMMARY OF THE PRESENT INVENTION

In one aspect of the present invention, a structural beam includes areinforcement beam having a length and mounts at ends of the beam andcross sectional shapes at various locations along the length, includinga first cross sectional shape near ends of the beam providing a firstbending moment and a second cross sectional shape at a center of thebeam providing a second bending moment different than the first bendingmoment, and further including intermediate cross sectional shapesbetween the ends and center having intermediate bending moments betweenthe first and second bending moments. The second cross sectional shapehas an identical profile to a portion of the first cross sectionalshape.

In another aspect of the present invention, a bumper reinforcement beamfor a vehicle bumper system, comprises a beam having a length and aplurality of transverse cross sectional shapes, with at least one crosssectional shape near a center of the beam defining a largest crosssectional shape and other of the cross sectional shapes being only aportion of the largest cross sectional shape, such that a first crosssectional shape near ends of the beam provides a first bending momentand a second cross sectional shape at a center of the beam provides asecond bending moment less than the first bending moment, andvehicle-frame-engaging mounts on ends of the beam.

In another aspect of the present invention, a method comprising steps ofproviding a blank with non-uniform edges, and forming the blank to forma beam having a length and ends and transverse cross sectional shapes atvarious locations along the length, including a first cross sectionalshape near ends of the beam providing a first bending moment and asecond cross sectional shape at a center of the beam providing a secondbending moment different than the first bending moment, and furtherincluding intermediate cross sectional shapes between the ends andcenter having intermediate bending moments between the first and secondbending moments. The method further includes attaching vehicle mounts toends of the beam.

In another aspect of the present invention, an apparatus includes ablank-forming device with trimming device to form a blank withnon-uniformities; and a forming device that forms a beam from the blank,the beam having a length and mounts at ends of the beam and transversecross sectional shapes at various locations along the length, includinga first cross sectional shape near ends of the beam providing a firstbending moment and a second cross sectional shape at a center of thebeam providing a second bending moment different than the first bendingmoment, and further including intermediate cross sectional shapesbetween the ends and center having intermediate bending moments betweenthe first and second bending moments.

In another aspect of the present invention, a method comprises steps ofroll forming a strip of material to form a first beam having a lengthand ends and a constant transverse cross sectional shape along thelength, and secondarily removing unwanted material from the first beamto form a modified beam having different transverse cross sectionalshapes at specific locations along the length, with each one of thedifferent transverse cross sectional shapes providing a desired beamtorsion strength and beam bending strength at the specific locations.

In another aspect of the present invention, a method comprises the stepsof roll forming a strip of material to form a first beam having a lengthand ends and a constant transverse cross sectional shape along thelength, providing a laser device, and generating a laser to selectivelycut away unwanted material from the first beam to form a modified beamhaving different transverse cross sectional shapes at specific locationsalong the length, with each one of the different transverse crosssectional shapes providing a desired beam torsion strength and beambending strength at the specific locations.

In another aspect of the present invention, a method comprises the stepsof roll forming a strip of material to form a first beam having a lengthand ends and a constant transverse cross sectional shape along thelength, and secondarily removing unwanted material from ends of thefirst beam to form a modified beam having different transverse crosssectional shapes at specific locations along the length, with each oneof the different transverse cross sectional shapes providing a desiredbeam torsion strength and beam bending strength at the specificlocations.

In another aspect of the present invention, a method comprises the stepsof roll forming a strip of material to form a first beam having a lengthand ends and a constant transverse cross sectional shape along thelength, and secondarily removing unwanted material from the first beamto form a modified beam having different transverse cross sectionalshapes at specific locations along the length, with each one of thedifferent transverse cross sectional shapes providing a desired beamtorsion strength and beam bending strength at the specific locations,wherein the step of removing the unwanted material includes forming arear surface on the beam's ends configured to support bumper attachmentbrackets for attaching the modified beam to a vehicle frame.

In another aspect of the present invention, a method comprises the stepsof roll forming a strip of material to form a first beam having a lengthand ends and a constant transverse cross sectional shape along thelength, and secondarily removing unwanted material from the first beamto form a modified beam having different transverse cross sectionalshapes at specific locations along the length, with each one of thedifferent transverse cross sectional shapes providing a desired beamtorsion strength and beam bending strength at the specific locations,wherein the step of removing the unwanted material includes forming afirst cross sectional shape near ends of the beam with a first bendingmoment, and forming a second cross sectional shape at a center of thebeam with a second bending moment different than the first bendingmoment, and further forming intermediate cross sectional shapes betweenthe ends and center having intermediate bending moments between thefirst and second bending moments.

These and other aspects, objects, and features of the present inventionwill be understood and appreciated by those skilled in the art uponstudying the following specification, claims, and appended drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1-3 are orthogonal views of a prior art bumper reinforcement beammade according to Sturrus U.S. Pat. No. 5,454,504; FIG. 4 is a top viewof the beam in FIG. 1 attached to a vehicle frame by mounts; and FIGS.5-6 are graphs illustrating a weight per longitudinal unit and a beammoment per longitudinal unit for the beam in FIG. 1, respectively.

FIGS. 7-9 are perspective, top and rear views of a B-shapedreinforcement beam having a varied moment of inertia along its lengthand embodying the present invention; and FIGS. 7A and 7B are perspectiveviews of a B-shaped reinforcement beam with modified end sections givingthe varied bending strength.

FIG. 10 is a rear view of the beam overlaid onto a flat blank beforeroll forming.

FIGS. 10A-10I are cross sections taken along lines 10A-10I in FIG. 10.

FIGS. 11-12 are graphs illustrating a weight per longitudinal unit and abeam moment per longitudinal unit, respectively.

FIG. 13 is a side view of the beam of FIG. 7 attached to a vehicleframe.

FIG. 14 is a side view showing an impact against the beam that isvertical offset upwardly on the beam, thus causing a torsional loadalong the beam.

FIG. 15 is a schematic view of the roll forming process using apre-pierced, pre-cut blank.

FIG. 16 us a plan view of a continuous strip pre-pierced and pre-cut toform series of blanks; and FIG. 16A is a plan view of a wider continuoussheet with a modified cut to form three adjacent strips of pre-piercedpre-cut blanks like those in FIG. 16 and with edges abutting to reducewasted material.

FIG. 17 is a flower diagram showing bending of a flat blank into thefinal shape of a B-shaped beam with varied bending moments as per FIG.7.

FIGS. 18-20 are top, rear and cross sectional views of a D-shaped beamhaving a varied moment of inertia along its length and embodying thepresent invention.

FIG. 21 is a top view of a second embodiment of the present inventivebeam.

FIGS. 22-23 are rear and front perspective views of FIG. 21.

FIG. 23A is a view of a modified beam similar to the beam in FIG. 23 butwith up and down flanges eliminated.

FIG. 24 is a top view like FIG. 21, but showing several cross sectionlines labeled 1-5.

FIG. 25 includes several perspective views taken along the cross sectionlines 1-5 in FIG. 24.

FIG. 26 is a plan view of a blank cut from an unrolled strip of sheetmaterial for forming the beam of FIGS. 21-25.

FIGS. 27A-27B, 28-29 disclose a beam similar to the beam in FIGS. 18-20,but made by using a modified method where a beam with constant crosssection is roll formed and then secondarily cut to have a shape like thebeam in FIGS. 18-20, FIGS. 27A-27B being top and end views of the beamprior to secondarily cutting away portions of the beam, and FIGS. 28-29being top and rear views of the beam after portions are secondarily cutaway.

DESCRIPTION OF PRIOR ART

Sturrus U.S. Pat. No. 5,454,504 discloses a prior art bumperreinforcement beam 10 (FIGS. 1-4) where the beam 10 is attached to avehicle frame by mounts (see FIG. 4). The beam 10 has a constant crosssectional shape, such that the beam 10 has a constant weight perlongitudinal unit (illustrated by the horizontal line 21 in FIG. 5) anda constant beam moment per longitudinal unit (illustrated by horizontalline 22 in FIG. 6). When the required bending moment is not constantalong a length of the beam, such as shown by dashed line 23, the beam'sbending moment 22 must still be designed to meet the maximum bendingmoment required. The beam 22 results in “excess” material at locations26 and 27 spaced from the center location 25, because material in thebeam 10 cannot be reduced even though the material is not needed to meetthe (lower) bending moment requirement at the ends. In other words, inFIG. 6, the beam 10 has “excess” material at end locations, resulting inexcess weight in the beam 10.

Sturrus U.S. Pat. No. 5,104,026 discloses in FIG. 2 a roll formed beamhaving an end crushed to a different shape with reduced cross section.However, all material remains in the beam. Sturrus U.S. Pat. No.6,240,820 discloses a roll formed beam with ends cut to different crosssection. However, the cut area is to provide a flat region for thevehicle mount and is limited to an area at the mount, and concurrentlydoes not substantially affect areas inboard of the mounts.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present bumper reinforcement beam 50 (FIGS. 7-9) includes a variedcross section and concurrently a varied bending moment along its length,due to a changing cross section that provides a lower bending momentnear ends 51 of the beam 50 (where the beam 50 is mounted to a vehicleframe 52 via mounts 53), and provides a higher bending moment near acenter location 54 (where the beam 50 requires a greatest bending momentto pass FMVSS bumper safety standards during vehicle bumper testing).The present beam 50 is referred to as a “C-D-C” beam since its crosssection changes from an open C-section at one end (FIGS. 10A-10C) to aclosed tubular (D) section near its middle (FIGS. 10D-10F) and then backto an open C-section at its other end (FIGS. 10G-10I). Notably, thefirst cross sectional shape near ends of the beam 50 has an identicalprofile but it is limited to only a portion of the second crosssectional shape at the beam's center. This facilitates forming the beamin a roll former to have optimal torsional and bending strength alongits length, but low total weight, as discussed below.

More specifically, near the mounts 53, the beam's bending moment doesnot need to be as large since impact forces against the beam 50 have arelatively short distance to the mounts, and thus impact forces aretransmitted relatively directly into the mounts (reducing the need for alarge bending moment). Contrastingly, near a center of the beam 50, thebeam's bending moment is necessarily relatively large, since impactforces against the beam 50 have a relatively longer distance to themounts, which thus requires a much larger beam bending moment. Theillustrated beam 50 is designed to accomplish this by being constructedfrom a blank 55 (FIG. 10) having a non-uniform width along its length.The blank 55 is rolled to form a tubular B (or D) section along itmiddle one-third, and to form open C sections along its outer one-thirdsat each end.

In FIG. 10, the beam 50 is overlaid on the blank 55 to show how portionsof the blank end up forming related portions of the beam 50.Specifically, one third of the illustrated beam 50 is formed by a centersection 56 of the blank 55 where the blank 55 has a generally constantwidth W1. The remaining one-third of the beam 50 is formed by endsections 57 and 58. The end sections 57 and 58 quickly narrow atlocations 59 to a width W2 and then generally taper inward toward anarrower width W3 at their ends. When roll formed, the center section 56forms a tubular B section with spaced-apart tubes 60 and 61, and the endsections 57 and 58 become open C sections with changing depths thinningtoward the outer ends of the beam 50. The sections 56, 57, and 58 sharea continuous constant-shaped front wall 59 with two channel ribs 60A and61A that extend a length of the beam 50. The front wall 59 extendsgenerally vertically, but the illustrated beam 50 is longitudinallycurved (i.e. “swept”) to match an aerodynamic shape often given modernvehicle front bumpers. The sections 56, 57, and 58 also share common topand bottom walls 62 and 63. The center section 56 also includes top andbottom aligned rear walls 64 and 65 and intermediate walls 66 and 67,each of which extend outward from the center section, and abutting walls68 and 69 that are welded to a center of the front wall 59. The specificcross sectional shapes along beam 50 are shown in FIGS. 10A-10I.

FIG. 11 is a graph illustrating a weight per longitudinal unit of thebumper reinforcement beam 50 of FIGS. 7-9, and FIG. 12 is a graphillustrating a beam moment per longitudinal unit of the beam 50 of FIGS.7-9. Notably, a weight of the innovative beam of FIGS. 7-9 is lower atends 51 of the beam 50 (see sections 56 and 57) than in a center (seelocation 58) due to cut-away material. The difference in weight of beam50 can be as much as 10%-20% less than prior art beams having a constantcross section (e.g. beam 10), including as much as 30-50% reduction inweight at ends 51 of the beam 50 from its center 58. Also, the bendingmoment varies along a length of the beam 50, with a lesser bendingmoment being adjacent the mounts 53, and a higher bending moment beingat the center 58. The difference in bending moment is substantial, sincethe required bending moment at the mounts 53 is essential zero sinceimpact loads at those locations are transferred directly through thebeam ends 51 into the mounts 53 without the beam ends 51 having toprovide stress resistance via a bending moment reactive force. However,at locations close to the center line 58A, a maximum bending moment isrequired because the center line 58A is located a maximum distance fromthe mounts 53, thus requiring the bending moment in order to provide anadequate resistive/reactive force.

Notably, the center line 58A has a relatively higher bending moment dueto additional material at the center (see the blank 55) and due to thecross section being tubular (which tends to have a higher bending momentdue to geometrical forces associated with the tubular shape) and has adeeper cross section. Contrastingly, the ends 51 have a relatively lowerbending moment due to less material at the ends (see blank 55) and alsodue to the fact that the cross section is an open C shape (which tendsto have a lower bending moment due to geometric forces associated withthe open shape) and has a thinner cross section.

It is noted that the pattern created by graphing the bending moment ofthe illustrated beam 50 (see FIG. 12) against locations along its lengthcreates a generally triangularly shaped curve with relatively flatangled side portions but with radiused center portion, with the bendingmoment continuously changing from zero at the ends 51 to a maximumnumber at the center line 58A. However, it is contemplated that specificcross sectional shapes and bending moments given to the beam at anyparticular location can be strategically set by carefully determining anoptimal shape of the blank for making the beam.

FIG. 13 illustrates a beam 50 mounted to a vehicle frame 52 at mounts 53at outer ends of the beam 50. FIG. 14 illustrates that an impactor 70may strike the beam 50 at a non-centered height (i.e. above itsmid-point, as shown in FIG. 14), such that the beam 50 may undergosignificant torsional loads. It is noted that these torsional loads donot necessarily correspond to the bending moment loads. In other words,even though the bending moment strength required of the beam 50 may bedifferent at different locations and define a first load curve, the beammust also withstand torsional loading requirements, which may bedistributed quite different than the bending moment requirements. Thepoint is that this information can be incorporated into a blank so thatwhen the beam is formed, an optimally shaped beam 50 results.

It is contemplated that the beam 50 can be made in different ways. Forexample, the beam 50 can be made solely by roll forming a blank having anon-uniform width, as discussed above (and see FIGS. 7-101).Alternatively, the beam 50 can be made using a combination of rollforming and secondary processing (see FIGS. 27A, 27B, 28-29). It iscontemplated that the roll formed continuous beam in this alternativeprocess can define an open constant cross section (such as a “C” or “L”or “I” shape), or can define a closed cross sectional shape (such as a“D” single tube, or “B” double-tube with single-center-leg or “B”double-tube with spaced-apart tubes). For example, as shown in FIGS.27A-27B, the beam of continuous constant cross section can be first rollformed, then swept (if desired), and then cut to a desired final shapeto form beam 50 by cutting away unwanted portions. FIG. 27A illustratesthe method as includes a laser device 120 generating a laser 121 thatcuts material along a desired line to remove triangularly-shaped (scrap)end pieces (see FIG. 28). However, it is contemplated that thetriangularly-shaped pieces can be any shape, any location on the beam,and can be done by other means, such as by stamping or plasma-cuttingaway parts of the beam. When stamping or mechanical shearing-off of thescrap end piece is done, a guillotine-style blade can be used, and ifnecessary, internal and external mandrels can be used to support the endof the beam to prevent undesired deformation of a cross section of theremaining-attached end portion of the beam. For the reader's benefit, werefer to Sturrus U.S. Pat. No. 6,510,771, the entire contents of whichare incorporated herein for its teaching and disclosure, which disclosesan end-cutting bumper-end-stamping operation.

Notably, the longitudinal curvature of beam 50 can be imparted into thebeam either as part of the roll forming process at a sweep station, orcan be imparted secondarily after the roll forming process such as bystamping. It is contemplated that a beam 50 including the up flange (seeup flange 106, FIG. 21) can be formed by cutting the beam 50 to includean extended flange that can be reformed in a secondary process toemulate up flange 106, discussed below. In one form, the constant crosssectional beam is roll formed with a straight flange that can bereformed/bent to define the desired up flange (106). In another form,part of a center of the beam is cut to leave a flange that can bereformed into the desired up flange.

FIG. 15 illustrates a roll forming process 80 including an unrollerdevice 81 feeding a roll of sheet 82 into a stamping device 83 (orirregular slitter) and then into a roll former 84 with rolls 85 forforming the beam 50 and then to a cutoff device 86. FIG. 16 illustratesa shape of the sheet 82 as it passes through the stamping device 83,where edges 87 of the sheet 82 are trimmed to remove waste material 88.It is contemplated that the stamping device 83 can leave the blanks 55interconnected at location 89, in which case the blanks 55 “lead” eachother through the roll former 84 and are cut apart at an end of theprocess. Alternatively, it is contemplated that the blanks 55 can beseparated at locations 89, in which case each blank 55 is fedindividually through the roll former 84. It is contemplated that asweeping station can be positioned at an end of the roll former 84, orthat a linear beam can be formed and then struck in a secondaryoperation to form the sweep in the beam 50.

FIG. 16A illustrates that the sheet 82A can be sufficiently wide forform multiple blanks 55 across its width in a manner reducing waste.Specifically, in sheet 82A, a wider part of one blank fits into aconcavity in adjacent blanks, thus reducing waste material cut from theblanks during the slitting process. It is noted that a laser slitter orother means for slitting a blank having a non-uniform width can be used.

FIG. 17 is a flower diagram showing bending of a flat blank 55 into thefinal shape of a B-shaped-cross-section beam 50 with varied bendingmoments as per FIG. 7.

FIGS. 18-20 are top, rear and cross sectional views of a D-shaped beam50A having a varied moment of inertia along its length and embodying thepresent invention. It is noted that a blank similar to blank 55 can beused to make a D-shaped beam 50A (swept or linear), with a center of thebeam 50A having a (single) tubular shape 95A and ends of the D-shapedbeam 50A defining a C channel section 96A. The beam 50A can belongitudinally swept or made to be linear.

A second embodiment beam 100 (FIGS. 21-25) is similar to the beam 50 interms of having a changing longitudinal cross sectional shape, but acenter region is left open and not formed into a tube. Thus, the presentbeam 100 is referred to as a “C-C-C” beam. Nonetheless, the center Csection extends a greater distance and thus provides a greater torsionaland bending strength than its ends. Also, material location andproperties are optimized.

Specifically, beam 100 includes a center section 101 and end sections102, formed by a front wall 103, top and bottom flanges 104 and 105, andup flange 106 and down flange 107. The illustrated front wall 103extends a full length of the beam 100, and includes a centered channel108 forming a rib along its full length. The illustrated channel 108includes a flat bottom and flat angled sides leading to the flat bottom,with the flat angled sides and bottom providing improved strength over asimilar channel having radiused sides and bottom. A cross sectional sizeand shape of the illustrated channel are constant along the full length.Nonetheless, it is contemplated that the channel can have a differentcross section or that the channel depth/shape can be varied along itslength. The top and bottom flanges 104 and 105 extend a full length ofthe beam, but are foreshortened near ends of the beam 100. Theillustrated flanges 104 and 105 are identical to each other, though itis contemplated that they do not need to be if there is a functionalreason to make them different shapes. The up flange and down flanges 106and 107 only extend a length of the center section 101, and arerelatively constant in their vertical dimension. The up and down flanges106 and 107 are identical to each other, though it is contemplated thatthey do not need to be if there is a functional reason to make themdifferent shapes. Mounting holes 109 for attaching the beam 100 to amount 110 (or for attaching to a crush tube 111 on a vehicle frame railtip) are provided.

FIG. 23 is a view of a modified beam 100A similar to the beam 100 inFIG. 23 but with up and down flanges (106, 107) eliminated.

In one form, a blank 112 (FIG. 26) for making beam 100 is cut (orstamped) from a strip of unrolled steel ahead of a roll formerapparatus, by removing scrap portions 114. Holes 109 can also be formedin the blank 112 at the same time. The ends of blanks 112 are leftconnected until after the roll forming operation, at which time theroll-formed beam segments are cut from each other. It is contemplatedthat the beam segments can be longitudinally swept by a sweep stationpositioned at an end of the roll former apparatus if desired.

In another form, a beam 50 (FIGS. 27A-27B) is formed having a continuousconstant cross sectional shape, and then secondarily reformed to removeunwanted material. As noted previously, the beam is swept if desired,either at an end of the roll forming process or in secondary tooling.Then the beam is then cut using a secondary process such as theillustrated laser device 120 that generates a laser 121 directed alongthe beam to cut away unwanted portions of the beam to leave a beam 50with varied torsional and bending strength along its length, as shown.As discussed previously, a stamping or other re-forming process can beused instead of a laser if desired.

It is to be understood that variations and modifications can be made onthe aforementioned structure without departing from the concepts of thepresent invention, and further it is to be understood that such conceptsare intended to be covered by the following claims unless these claimsby their language expressly state otherwise.

1. A bumper reinforcement beam comprising: a beam having a length andmounts at ends of the beam, the beam having transverse cross sectionalshapes at various locations along the length, including a first crosssectional shape near ends of the beam providing a first bending momentand a second cross sectional shape at a center of the beam providing asecond bending moment different than the first bending moment, andfurther including intermediate cross sectional shapes between the endsand center having intermediate bending moments between the first andsecond bending moments, the second cross sectional shape having anidentical profile to a portion of the first cross sectional shape. 2.The bumper reinforcement beam defined in claim 1, wherein the firstcross sectional shape defines an open channel, and wherein the secondcross sectional shape includes at least one tube.
 3. The bumperreinforcement cement beam defined in claim 1, wherein the first crosssectional shape defines a C shape, and wherein the second crosssectional shape defines a B shape.
 4. The bumper reinforcement beamdefined in claim 1, wherein the first cross sectional shape includes atleast one first C-shape section, and wherein the second cross sectionalshape defines at least one second C-shape section, the first and secondC-shape sections being different depths.
 5. The bumper reinforcementbeam defined in claim 4, wherein the first cross sectional shape definesa shallow open section, and wherein the second cross sectional shapedefines a deeper open section.
 6. The bumper reinforcement beam definedin claim 5, wherein the second bending moment is greater than the firstbending moment. 7-17. (canceled)
 18. A bumper reinforcement beam for avehicle bumper system, comprising: a beam having a length and aplurality of transverse cross sectional shapes, with at least one crosssectional shape near a center of the beam defining a largest crosssectional shape and other of the cross sectional shapes being only aportion of the largest cross sectional shape, such that a first crosssectional shape near ends of the beam provides a first bending momentand a second cross sectional shape at a center of the beam provides asecond bending moment less than the first bending moment; andvehicle-frame-engaging mounts on ends of the beam.
 19. The bumperreinforcement beam defined in claim 18, wherein the first crosssectional shape defines an open channel, and wherein the second crosssectional shape includes at least one tube.
 20. The bumper reinforcementbeam defined in claim 19, wherein the vehicle-frame-engaging mounts arecoupled with the ends of the beam, such that a torsional strength issubstantially uniform from an impact along the length of the beam. 21.The bumper reinforcement beam defined in claim 1, wherein the firstcross sectional shape defines an open channel, and wherein the secondcross sectional shape includes at least one tube.
 22. The bumperreinforcement beam defined in claim 1, wherein the ends of the beam areconfigured to engage a vehicle frame, such that a torsional strength issubstantially uniform from an impact along the length of the beam. 23.The bumper reinforcement beam defined in claim 18, wherein the firstcross sectional shape defines a C shape, and wherein the second crosssectional shape defines a B shape.
 24. The bumper reinforcement beamdefined in claim 18, wherein the first cross sectional shape includes atleast one first C-shape section, and wherein the second cross sectionalshape defines at least one second C-shape section, the first and secondC-shape sections being different depths.
 25. The bumper reinforcementbeam defined in claim 18, wherein the first cross sectional shapedefines a shallow open section, and wherein the second cross sectionalshape defines a deeper open section.
 26. The bumper reinforcement beamdefined in claim 18, wherein a blank with non-uniform edges is rollformed into the beam, and wherein the non-uniform edges are shaped toprovide the first and second cross sectional shapes.
 27. The bumperreinforcement beam defined in claim 26, wherein the blank includes afirst longitudinal edge and a second longitudinal edge that aresubstantially mirror images of each other along a longitudinalcenterline of the blank.
 28. The bumper reinforcement beam defined inclaim 27, wherein the non-uniform edges are shaped to provide the firstcross sectional shape with at least one first C-shape section and thesecond cross sectional shape with at least one second C-shape section,the second C-shape section having a deeper open section than the firstC-shape section.
 29. The bumper reinforcement beam defined in claim 27,wherein the first and second longitudinal edges are simultaneously rollformed toward each other to interconnect at the center of the beam todefine a B-shape section and to be spaced apart at the ends of the beamto define C-shape sections.